Optical proximity detectors (which can also be referred to as optical proximity sensors or optical proximity detection sensors) typically include or use a light source and an adjacent photosensitive light detector. Such optical proximity detectors can be used to detect the presence of an object, estimate proximity of (e.g., distance to) an object and/or detect motion of an object, based on the light originating from the light source that is reflected from an object and detected by the light detector. Where such detectors are specifically used to detect distance to an object, they can also be referred to as optical distance detectors or optical distance sensors. Where such detectors rely on time-of-flight (TOF) principles to detect distance to an object, they can also be referred to as optical TOF sensors, optical TOF proximity sensors, optical TOF proximity detectors, or the like. The value of these detectors/sensors has become more important with the advent of battery-operated handheld devices, such as mobile phones. For example, a fair amount of the energy from a mobile phone battery is used to drive the display, and there is value in turning off the display or backlight when the mobile phone or other device is brought to the user's ear (where it cannot be viewed anyway). Optical proximity detectors have been used for this, and many other applications.
For other examples, there are many other applications in which the presence of an object can be detected with an optical proximity detector to advantage. These range from sensing when protective covers have been opened on machinery, paper has been positioned correctly in a printer, or an operator's hands are at risk near an operating machine. An optical proximity detector can also be used as a simple touch or near-touch activated switch, and could be implemented in applications like keyboards or devices that have a plastic housing that is sealed but which allows the light from the source to pass through and be sensed by the detector on the return.